Fibrous structures, such as paper webs, are well known in the art and are in common use today for paper towels, toilet tissue, facial tissue, napkins, wet wipes, and the like. Typical tissue paper is comprised predominantly of cellulosic fibers, often wood-based. Despite a broad range of cellulosic fiber types, such fibers are generally high in dry modulus and relatively large in diameter, which may cause their flexural rigidity to be higher than desired. Further, wood fibers can have a relatively high stiffness when dry, which may negatively affect the softness of the product and may have low stiffness when wet, which may cause poor absorbency of the resulting product.
To form a web, the fibers in typical disposable paper products are bonded to one another through chemical interaction and often the bonding is limited to the naturally occurring hydrogen bonding between hydroxyl groups on the cellulose molecules. If greater temporary or permanent wet strength is desired, strengthening additives can be used. These additives typically work by either covalently reacting with the cellulose or by forming protective molecular films around the existing hydrogen bonds. However, they can also produce relatively rigid and inelastic bonds, which may detrimentally affect softness and absorption properties of the products.
The use of synthetic fibers along with cellulose fibers can help overcome some of the previously mentioned limitations. Synthetic polymers can be formed into fibers with very small fiber diameters and are generally lower in modulus than cellulose. Thus, a fiber can be made with very low flexural rigidity, which facilitates good product softness. In addition, functional cross-sections of the synthetic fibers can be micro-engineered as desired. Synthetic fibers can also be designed to maintain modulus when wetted, and hence webs made with such fibers resist collapse during absorbency tasks. Accordingly, the use of thermally bonded synthetic fibers in tissue products can result in a strong network of highly flexible fibers (good for softness) joined with water-resistant high-stretch bonds (good for softness and wet strength). However, synthetic fibers can be relatively expensive as compared to cellulose fibers. Thus, it may be desired to include only as many synthetic fibers as are necessary to gain the desired benefits that the fibers provide.
Thus, it would be advantageous to provide improved fibrous structures including cellulosic and synthetic fibers in combination, and processes for making such fibrous structures. It would also be advantageous to provide a product that has synthetic fibers concentrated in certain desired portions of the resulting web and a method to allow for such non-random placement of such fibers.